The invention relates to a cylindrical body that at the outer periphery is provided with means for counteracting vibrations occurring in that body, both in the direction of flow and perpendicular to it, which result from a transverse flow against it.
The invention is in particular of importance for application in constructing bunches of tubes in heat exchangers, pipe lines in rivers, piers of oil rigs, suspension cables or pillars of bridges, chimneys and the like.
In such bodies vibrations are caused by periodically simultaneously or, alternatingly to the left and to the right of the cylindrical body, shedding of vortices that are carried along with the flow and which are formed each time simultaneously or alternately at either side of this body and behind it.
If the frequency of shedding of these so-called von Karman vortices corresponds with the own frequency for bending vibrations of the cylindrical body, as a result of amplification such great amplitudes may arise, that by fatigue or overloading breakage will occur in this cylindrical body.
Violent vibrations will occur if shedding of vortices over greater lengths of the cylindrical body will occur simultaneously, so that great resulting oscillating bending moments affect this body.
It has been proposed in the art to reduce the vibrations in chimneys, pipe constructions and the like occurring as a result of transverse flow, by application of long helical ribs at the periphery of such pipe constructions.
These helical ribs, however, form a great angle with the cross-section of these pipe constructions and the application of these ribs will increase the average resistance of a cylindrical body to a considerable extent.
In case of overcritical conditions of flow it will be possible that this resistance even increases by a factor of from 2 to 3.